An HPLC method on C18 column using a gradient mobile phase is proposed for the separate determination of residual benzoyl peroxide (BP) and benzoic acid (BA) in flour and wheat products. The recoveries obtained were quite excellent, from 96.0 to 99.3% for BP added to the flour, and 91.3% for BA added to the flour. Analysis of 10 samples of commercial foods such as flour and wheat products, detected 0.7 microg/g of BP in imported noodles. Furthermore, we successfully verified the existence of BP by LC-MS. These methods are simple and reliable for determination and verifying the amount of BP and BA in foods since now the use of BP as a food additive is permitted in many countries.